1. Field of the Invention
The present invention relates to an illumination optical system for enlarging an image displayed on image display means such as a liquid crystal display panel or micromirror device panel and projecting thus enlarged image onto a screen, and a projector apparatus using the same; and, in particular, to an improvement in the relative positional relationship between the image display means and an integrator section for homogenizing the illumination of light illuminating the image display means, and an improvement in their structures.
2. Description of the Prior Art
In illumination optical systems for liquid crystal projectors, there has conventionally been known a technique using an optical system which employs an integrator for eliminating unevenness in illumination on liquid crystal display panels.
Namely, such an illumination optical system comprises a first integrator plate (generally known as second flyeye or the like), a second integrator plate (generally known as first flyeye or the like), and a field lens successively disposed in this order downstream a light source section using a reflector. The first integrator plate is constituted by a plurality of lens elements, each having a form substantially analogous to that of a liquid crystal display panel, which are arranged two-dimensionally, and splits a luminous flux having a relatively higher degree of unevenness in brightness emitted from the light source section into partial luminous fluxes by the number identical to that of the lens elements in the first integrator plate. Thus obtained partial luminous flux has a lower degree of unevenness in brightness as compared with the luminous flux before being split. By means of the second integrator plate and the field lens, the individual partial luminous fluxes are emitted toward an area to be illuminated, so as to be superposed on one another, whereby it is possible to realize illumination with less unevenness in brightness.
Meanwhile, though it is desirable for the optical system using an integrator to be designed such as to secure an illumination area which is large enough to absorb influences of errors in manufacture of the integrator itself or mirrors, lenses, and the like disposed on the optical path, it is important that the form of the illumination area be basically made slightly larger than the liquid crystal display panel at most, so as to minimize the decrease in illumination efficiency.
On the other hand, since the projection lens employed in a liquid crystal projector is often used as being shifted in a direction perpendicular to the optical axis of its liquid crystal display panel, it is generally designed such that its liquid crystal side is formed into a telecentric system. Also, in conjunction therewith, the illumination optical system using an integrator is generally designed as a system in A which the luminous flux becomes telecentric after passing through the liquid crystal display panel. When such a telecentric system is formed, however, it may be problematic in that a large number of lenses are needed as the projection lens, each lens has a larger diameter, and so forth, thereby increasing the size and cost of the apparatus.
Therefore, the conventional illumination optical system using an integrator employed in the liquid crystal projector may simply be inclined as a whole with respect to the liquid crystal display panel, so that the luminous flux emitted from the liquid crystal display panel forms a predetermined angle with its normal, thereby constituting a so-called non-telecentric system.
When the illumination optical system is simply arranged so as to be inclined as a whole with respect to the liquid crystal display panel, however, since each lens element of the first integrator panel, i.e., the integrator plate on the light source side has a form analogous to that of the liquid crystal display panel as mentioned above, the illumination area expands in a direction along which extends the line of intersection formed between the first integrator plate and the plane including the optical axis of the integrator and the normal of the liquid crystal display panel, thereby lowering the illumination efficiency.
As image display means, attention has recently been given to the micromirror device panel (DMD) in which a plurality of micromirror devices are arranged. In the micromirror device panel, it is necessary that a luminous flux be made obliquely incident thereon while forming a predetermined angle with the normal of the panel. Therefore, in the case where such a micromirror device panel is used as the image display means, the decrease in illumination efficiency may be problematic as with the case using the liquid crystal display panel.